Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$186.33	12.483%	$209.5896	$209.59	$209.60	$209.60
Purchase #2	$199.86	6.183%	$212.2173	$212.22	$212.20	$212.20
Purchase #3	$104.69	12.493%	$117.7689	$117.77	$117.75	$117.80
Purchase #4	$116.49	3.504%	$120.5718	$120.57	$120.55	$120.60
Purchase #5	$37.31	13.571%	$42.3733	$42.37	$42.35	$42.40
Purchase #6	$118.27	7.510%	$127.1521	$127.15	$127.15	$127.20
Purchase #7	$89.47	4.231%	$93.2555	$93.26	$93.25	$93.30
7 purchase totals =	$852.42		$922.9285	$922.93	$922.85	$923.10